1. Field of the Invention
The present invention relates to a wire bonding method for the manufacture of semiconductor devices, etc.
2. Prior Art
In wire bonding methods, as is well known, bonding is performed by pressing a wire (passed through a tool) onto a bonding point.
Conventionally, the bonding load which presses the tool against the bonding point has been viewed as a load which can be set arbitrarily (for example, such loads are described in Japanese Patent Application Laid-Open No. 53-45970 and Japanese Patent Application Publication No. 63-50856).
Such wire bonding mechanisms have a load-supplying means which includes a solenoid coil and an iron core which is positioned inside the solenoid coil. During lowering and raising of the tool, a load which is larger than the bonding load (hereinafter called "pre-loading load") is applied so that a transducer which holds the tool at one end follows a cam which drives the transducer.
In a bonding method which uses such a bonding device, the tool is lowered in a pre-loaded state, and the load is changed to the bonding load (which is smaller than the preloading load) after the tool has contacted the bonding point. An ultrasonic oscillating output is output, and bonding is performed with the wire pressed against the sample under the bonding load.
In the above-described prior art, the tool contacts the bonding point under the pre-loading load (large load). The impact load which is generated at the time of this contact accompanies the lowering action of the tool and is therefore larger than the pre-loading load. When this large impact load is applied to the sample, damage such as cracks, cratering, etc. may result. Furthermore, if the impact load which is applied when the tool contacts the bonding point is large, the transducer holding the tool will vibrate. As a result, a uniform load cannot be applied to the bonding point from the tip of the tool. Accordingly, the aforementioned ultrasonic oscillating output is applied in a state of fluctuating load, which has a deleterious effect on bondability.